Controls of the variations of individual and multiple ecosystem functions following shrub encroachment
Plant cover, species richness, AGB and BGB were significantly related with SW, NO3−N and NH4+−N contents (Fig. 5). The SOC and STN contents also had significant relationship with BGB, SW, NO3−N and NH4+−N. In pooled all data together, we found that SR, AGB, SW, STN, MBC, and NO3−N had significant relationships with the overall and above- and belowground ecosystem multifunction indexes of the alpine steppes (Fig. 5). We further found that the RII indexes of plant productivity, soil microbial biomass, and soil nutrients had positive relationships with that of the ecosystem multifunction indexes (Fig. 6), suggesting that plant productivity, soil microbial activity, and soil nutrients play critical roles in driving ecosystem functioning responses to shrubs encroachment (Fig. 7). However, the RII index of EMF indicated that there were no significant relationships between EMF and that of SR and SW (Fig. 6). For different apart of the ecosystem functions, the RII indexes of AEMF and BEMF both yielded positive and significant relationships with that of the plant cover, AGB, BGB, SW, SOC, and NO3−N (Fig. 6).